Soil Potassium Availability to Corn and Soybean in Minnesota Assessed Using Field Moist Soil Samples.

Issue related to drying of soil samples prior to analysis of K have resulted in a need for the evaluation of soil testing methods for K in the upper Midwest. Results from Iowa have shown a better correlation between corn (Zea mays L.) and soybean [Glycine max. (L.) Merr] yield response and K extracted by ammonium acetate when analyzed on field moist soil samples. The purpose of this work was to evaluate the amount of K extracted by ammonium acetate for air dried versus field moist samples and to correlate crop response to K extracted by the two methods. Soil samples were analyzed from strip trial and small plot studies where samples were collected Spring or early Summer from plots where K was not applied. Soil was sampled at a 15 cm depth, were sieved and split to air dry half of the sample and keep the rest at field moist state, then K was extracted with 1M ammonium acetate solution at a ratio of 1:10 (soil: solution) for 5 minutes. The amount of K extracted based on analysis method varied among soils. More K was extracted using field moist samples for silt loam soils, less K was extracted on moist soils for loam and clay loam soils, and there was little difference in extraction methods for sandy soils.